This proposal is aimed at studying signaling-dependent neuroadaptations that occur in response to ethanol in subpopulations of neurons within the dorsomedial striatum (DMS). The DMS plays a central role in goal- directed behaviors and addiction, and we found that voluntary and passive exposure of rodents to ethanol activates the tyrosine kinase Fyn specifically in the DMS. We further discovered that in response to ethanol, activated Fyn phosphorylates the NR2B subunit of the NMDARs (GluN2B) resulting in increased synaptic activity of NMDA and AMPA receptors (NMDAR/AMPAR). Finally, we showed that the Fyn-signaling pathway in the DMS plays a crucial role in mechanisms underlying ethanol-drinking behaviors. Neurons in the DMS express either dopamine (DA) D1 or D2 receptors (D1R, D2R) that form the direct Go and indirect No-Go pathways. Thus, DA is thought to have different and possibly opposite effects on D1R and D2R neurons. D1Rs are coupled to G protein ?s (Gs), which activates cAMP/PKA signaling, whereas D2Rs are coupled to Gi, which inhibits cAMP/PKA. We found that Fyn activation depends on cAMP/PKA, and that in vivo administration of a D1R agonist but not D2R agonist activates Fyn signaling in the DMS, and specifically in D1R DMS neurons. Together, these data suggest the DA activates a signaling pathway consisting of D1R/Gs/Fyn/GluN2B/AMPAR in D1R neurons. Ethanol increases DA levels in the striatum, and we hypothesize that ethanol activates Fyn signaling specifically in D1R neurons in the DMS to facilitate neuroadaptations in the direct Go pathway that drive ethanol drinking behaviors. We also hypothesize that remote activation of Gs signaling in D1R DMS neurons is sufficient to produce similar Fyn-dependent cellular and behavioral neuroadaptations. These hypotheses will be tested in vivo using transgenic mice that express Cre in D1R or D2R neurons, and will utilize innovative molecular and chemico- genetic approaches to manipulate single genes (Cre-FLEX), and to remotely activate Gs signaling using the Designer Receptors Exclusively Activated by Designer Drugs (DREADD) method in specific subpopulations of neurons. Aim 1 and Aim 2 will determine whether Fyn-dependent adaptations induced by ethanol occur in D1R, but not D2R, neurons in the DMS, and whether Gs DREADD activation in DMS D1R neurons is sufficient to produce similar outcomes. Aim 3 will investigate the contribution of Fyn signaling in D1R DMS neurons to ethanol drinking behaviors, and whether Gs DREADD activation of Fyn in D1R is sufficient to produce ethanol seeking and drinking. Combining Molecular and Systems Neuroscience methodologies, we will unravel cell- type specific signaling adaptations that underlie the development and maintenance of ethanol drinking and seeking behaviors.